The present invention relates to a calibration method, calibration apparatus, and memory medium storing the calibration method of a printer, and in further detail, relates to an improvement of a color reproduction method of the printer.
For example, in the color printer, the color reproduction is realized by the following method. FIGS. 5(a) to 5(d) are illustrations of the color reproduction method of the printer. In the drawings, FIG. 5(a) and FIG. 5(b) are illustrations of the conversion of the reproduction color (output), and FIG. 5(c) and 5(d) are illustrations of the conversion of the target color (input).    (1) By measuring many number of color patches, the relationship of a set of calorimetric values for the combination of the color material is made. Herein, the color material means the color material of Y, M, C, and BK etc.
Initially, the relevant printer is used and many color patches are printed. FIG. 5(a) shows the Y and M space expressed by 2 dimensions. Herein, the space of Y, M, C, (BK) is expressed by 2 dimensional Y and M spaces for the simplification. Values of lattice points in the Y direction and the M direction are respectively defined as 0, 64, 128, 192, 255 as shown in the drawing. These Y, M values of 5×5 lattice points are inputted into the printer, and color patches are made.
When the color patch printed by the combination of these Y and M is color-measured, the value of the colorimetry is obtained as the 3 stimulus values X, Y, and Z. The values obtained in this manner are converted into the other color system (for example, L*a*b*, L*u*v*). When these are plotted into the L*C* color system (uniform color space) in this manner, the space shown in FIG. 5(b) is formed. This space shows the proper space (color solid) to the using printer. Herein, L* is lightness, and C* is chroma. Herein, a, b, c, and d of the spaces of FIG. 5(a) correspond to a′, b′, c′, and d′ of FIG. 5(b). In this manner, to make the space of the color system (calorimetric value) from the Y, M spaces (color material) is called the characterization by the multi-dimensional LUT.    (2) Next, the combination of the color material amount (or system value) of the printer to the target color is obtained.
Next, also for the R, G, B spaces showing the target color, as shown in FIG. 5(c), the same kind of space (color solid) as the case of FIG. 5(a) is made. Herein, for the simplification, the spaces of G and B are made. Also for the combination of G, B which is a color material herein, the lattice points of the space of 5×5 are found, and when the values of lattice points of these spaces are plotted in the color system, the color solid space as shown in FIG. 5(d) is obtained.
When the L*C* space as shown in FIG. 5(d) is formed, the target color is determined by using FIG. 5(c). The target color is defined as m1 as shown in FIG. 5(c). The corresponding area of the space shown in FIG. 5(d) corresponding to this m1 is obtained, and the point m1′ in its corresponding area is obtained.
After m1′ is obtained, the point m1″ which is corresponding to m1′ in the L*C* space of the reproduction color system is obtained. When the point m1″ is obtained, the corresponding point m1′″ in the Y, M spaces of the reproduction color system in FIG. 5(a) is obtained. In this manner, when the reproduction color is obtained from the target color, since the relationship of the reproduction color to the target color is determined, the conversion table (color conversion LUT) of G, B→Y, M is made. These color conversion tables are made by the number of target colors. According to this process, when the target color is given by G, B, the reproduction color is given by M and Y.
In this manner, to obtain the combination of the color material (or system value) of the printer corresponding to the target color, is called the color matching.    (3) Next, the step of (2) is repeated, and the table (color conversion LUT) showing the relationship of the color material (or system value) of the printer to each combination of the input signal is made.    (4) By using the color conversion LUT (color matching table) made in this manner, the image data is printed by the printer.
When such a series of the sequence is conducted, the correct image can be printed by the printer such that the relationship of the reproduction color to the target color is exactly represented. By this method, even when there is a deviation in the color conversion characteristics of each of printers, in the process to plot in the L*C* space shown in FIG. 5(a) to FIG. 5(b), the individual difference of each printer is removed, and the image of the correct reproduction color can be printed without depending on the printer individual.
As the reference art relating to the above described color conversion, the following are well known. Japanese patent No. 2895086: In the calculation method of above (2), the space is divided into triangular pyramids and the target color material value is obtained at high speed.
Japanese patent No. 2554366: In the four-color printer, as black is increased, the color patches subjected to the colorimetry are decreased.
Japanese patent No. 2952489: By using black at the maximum in the four-color printer, the colorimetry points are decreased (maximum black method).
Japanese patent application No. 2000-281161: the color reproduction method of the special color. The color data is divided into a plurality of 4 dimensional color areas and the color is structured.
When the printer characteristic is varied, a method to correct only the gradation curve is well known. FIG. 6 is a conceptual view of the color reproduction system. When the data of R, G, B are outputted from the input device 1, they enter into the 3 dimensional LUT 2, and the conversion from the R, G, B system to the Y, M, C system is conducted. For the output of each of Y, M, C, the LUT 3—LUT 5 to conduct only the gradation conversion are provided. From each of LUT 3—LUT 5, the Y′, M′ and C′ whose gradations are converted, are outputted, and they enter into the printer 6, and the image is printed.
Herein, when the printer is varied, the change is not added to the 3 dimensional LUT 2, and when only the gradation LUT 3—LUT 5 provided on the output side of each of Y, M, C are corrected, the influence by the variation of the printer is lightened. In the case where this method is used, when the primary color point is not changed, the general color reproduction can be obtained. Herein, the primary color point is the lattice points (a′, b′, c′, d′) of four corners of the color system shown in FIG. 5(b).
For example, in the ICC profile (International Color Consortium), the gradation can be corrected in the profile, and by using this, the correction of the profile can be conducted.
When the characterization is conducted in the LUT form shown in the method as described above, it is necessary that a numerous color patches are measured, and when the characteristic variation of the printer is generated, it is necessary that the whole are measured again.
Further, in the case where the correction to the characteristic variation of the printer is conducted by only the gradation curve, for example, when the maximum density is lowered, or media condition (for example, the printer sheet of the ink jet printer) is changed, the calorimetric value of the primary color is changed, and there is a problem that the correct color is not reproduced. Particularly, in the print onto the cloth, for the purpose of the industrial use, which needs to output the color in the absolute value (for example, L*a*b* value), such a problem is not allowed. Therefore, it is necessary to measure again, and particularly, it takes a long period of time for the colorimetry.
For example, it is necessary that the color is measured for (5×5×5=125) points in the 3-color printer, (5×5×5+5×5×5+3×3×3+3×3×3+2×2×2=312) points in the 4-color printer, and for the 7-color hifi color, the color measuring is necessary for the color patches of 4 times of it. In this connection, the number of measurement shown herein is an example. Further, when the medium is the paper, it can be automatically measured by the calorimeter with the xy stage (the calorimeter which can automatically move in the xy direction), however, for the cloth, such an automatic measurement is difficult, and the manual measurement is necessary.
In view of such a problem, the present invention is attained, and the object of the present invention is to provide a calibration method, a calibration apparatus, and a memory medium storing the calibration method of the multi-color printer, wherein the variation of the printer (media) is absorbed by the minimum additional colorimetry and correct color reproduction can be performed.